TASK DIFFICULTY MODULATES THE ACTIVITY OF SPECIFIC POPULATIONS OF NEURONS IN PRIMARY VISUAL CORTEX
Spatial attention enhances our ability to detect stimuli at restricted regions of the visual field. This enhancement is thought to depend on the task difficulty but the underlying neuronal mechanisms for this dependency remain largely unknown. In this talk I will show evidence that task difficulty strongly modulates neuronal firing rate at the earliest stages of cortical processing (area V1), and that these modulations are spatially specific: increasing task difficult enhances V1 neuronal firing rate at the focus of attention and suppresses it in regions surrounding the focus. Moreover, I will show that response enhancement and suppression are mediated by distinct populations of neurons that differ in direction selectivity, spike width, interspike interval distribution and contrast sensitivity. Our results provide strong support for center-surround models of spatial attention and suggest that task difficulty modulates the activity of specific populations of neurons in the primary visual cortex.
